The present invention relates to a sharpening unit for leather splitting machines.
It is known that for carrying out the splitting of leather and the like, that is in order to perform a transverse cutting along leather sheets and separate a valuable layer having a constant thickness from a less valuable one to be discarded and corresponding to the reverse side of said sheets, particular machines referred to as splitting machines are used, which machines accomplish a leather thinning cut by means of band blades tautened between two pulleys or flywheels.
Due to the fact that leathers to be split are usually very thin in thickness, the band blade must be capable of operating in a very precise manner and consequently the cutting edge or bevel thereof must always be perfectly sharpened. To achieve a perfect sharpening a sharpening unit is provided to be mounted on splitting machines which unit must act continuously, during the machine operation, by means of a pair of grinding wheels symmetrically disposed relative to the blade bevel and in contact therewith.
Grinding wheels conventionally used on leather splitting machines consist of a mixture of abrasive materials with differently sized grains and must be provided with independent adjusting means designed to adjust their positioning in relation to the blade bevel. In greater detail the upper and lower grinding wheels are mounted on respective swinging arms provided with a projection in which a threaded through hole is bored. Operatively engaged with said hole is an adjusting screw the free end of which is designed to abut against a fixed locator element carried by the sharpening unit casing. In this manner, by acting upon one of the adjusting screws it is possible to move the swinging arm supporting the respective grinding wheel as far as the latter reaches the correct positioning relative to the blade bevel.
While the splitting machine is running an operator must intervene rather often on the adjusting means both because it is necessary to have a constant control on the bevel wear and because the operative surface of the grinding wheels must be periodically dressed.
More particularly, the grinding wheel dressing operation brings about a reduction in the diameter of the grinding wheels themselves so that the working surfaces thereof move apart from the cutting blade. Obviously, as a result, it becomes necessary to carry out a resetting of the adjustment.
In order to eliminate the drawbacks resulting from the wear of the working surfaces in grinding wheels which give rise to dirtiness and involve periodical adjusting interventions, in traditional splitting machines grinding units have been used which are provided with diamond grinding wheels, that is particular grinding wheels which, although exerting an excellent abrasive action, are noiseless and subjected to a minimum degree of wear, at all events much more reduced than traditional grinding wheels.
All attempts to use diamond grinding wheels in leather splitting machines have however given poor results, due to a series of inconveniences among which one of the most important is the fact that said diamond grinding wheels are mounted on the same supporting structures as those used for traditional grinding wheels made of abrasive material. In fact, owing to the weak wear of said diamond grinding wheels and to the fact that the adjustment of the lower grinding wheel is independent of that of the upper one, the operator cannot visually see whether both grinding wheels exert their abrasive action on the blade bevel in identical manner and correctly. Practically, in the absence of the characteristic "flashing" caused by the abrasive action of traditional grinding wheels on the blade, the operator cannot realize whether one grinding wheel is working more than the other and consequently whether the bevel is symmetric and is carrying out a correct cutting of the leather. In addition, still due to the independent adjustment of the grinding wheels, the same difficulties as regards positioning and possibilities of repeated positionings as already found in sharpening units provided with traditional grinding wheels, are present here as well.